Associate Professor Dr. Nguyen Minh Ngoc (Director of the Green Materials Research and Application Center, GTS InnoLab Co., Ltd.) and his team at the Vietnam Petroleum Institute and Vietnam Petroleum University have conducted research on the heat exchange process in a rotary reactor with shredded tire rubber. Their work aims to develop an efficient pyrolysis process for large-scale applications. This outcome will decrease heat processing duration, lower fuel expenses, enhance heat exchange processes, optimize gas collection, and boost the oil yield from recycled materials.
Ever since the birth of the rubber industry, we've been grappling with the question of what to do with all the rubber waste. With the surge in waste materials, like rubber, that don't break down easily, managing and disposing of rubber waste has become a pressing matter. For instance, in Ba Ria - Vung Tau province, over 100 tons of worn-out tires are gathered daily from automotive repair shops, as mentioned by Associate Professor Dr. Nguyen Minh Ngoc, the Director of the Center for Green Materials Research and Application at GTS Innolab Co., Ltd.
Various measures have been implemented to leverage raw material sources or mitigate the environmental impact of waste like old tires and plastics. However, Dr. Nguyen Manh Huan from the Vietnam Petroleum Institute says, "Recycling facilities for these materials often rely on empirical methods rather than precise calculations, resulting in significant limitations in the pyrolysis process." These limitations lead to reduced recovery efficiency of valuable raw materials such as oil and carbon black and cause excess heat from condensed gases to be wasted, contributing to secondary emissions. Additionally, the pyrolysis process tends to be longer.
This issue led Dr. Nguyen Minh Ngoc and engineers at DVA Renewable Energy Plant (DVA Plant), part of the ecosystem with GTS InnoLab, to collaborate on developing a more optimized pyrolysis process. The goal is to enhance efficiency, improve product quality, and ensure fire and explosion safety throughout the pyrolysis technology chain.
As Dr. Nguyen Minh Ngoc, Associate Professor, has pointed out, there's been a plethora of research on thermal issues but a noticeable lack when it comes to practical applications for old tire pyrolysis furnaces. This includes heat processing diagrams that illustrate the relationship between time and temperature for each pyrolysis phase (heating, maintaining heat, cooling). As such, their main objective is to determine the heat generated by the burning of surplus GAS fuel, the temperature within the combustion chamber, the external temperature, and the temperature within the reactor's shell. They are also aiming to enhance heat transfer and efficiency when slicing tires and to improve the aerodynamics of hot air flow. Moreover, they plan on creating heat processing charts and material conservation charts, and implementing heat calculation results in practical applications at factories, common control centers, and processing centers. This includes a sensor measuring system for temperature, pressure, and the volume of oil and gas formed during heat processing.
The amount of heat absorbed by waste rubber tire materials is significantly influenced by factors such as the heat source, heat transfer method (radiation, convection, conduction), and particularly the shape and size of the tires. Increasing the heat source contact area by machining and cutting the tires into smaller pieces can enhance heat absorption. To perform calculations, the research team utilized the technical parameters from the DVA factory. The rotary reactor used for pyrolyzing old car tires at the DVA factory has a cylindrical shape with a diameter of 3000 mm and a length of 7000 mm. During the pyrolysis process, the temperature generated by burning GAS in the combustion chamber heats the furnace's outer shell, which is made of 22 mm thick A515 alloy steel.
The temperature inside the pyrolysis furnace gradually rises to over 600°C (estimated based on calculations). The furnace is fully sealed to prevent oxygen from entering, which could cause fire or explosion. The surface temperature of the furnace shell is transferred to the raw tire material, raising it to 500°C, where it produces volatile substances, a mixture of carbon and hydrogen gases (CH). The gas flow is extracted and condensed to form Tire Pyrolysis Oil (TPO), which constitutes about 48% of the input material. Non-condensable gases and residual GAS account for approximately 14-15% and are used to fuel the furnace.
“The Board of Directors and the technical team have invested significant effort into designing and manufacturing supporting equipment, modifying the working principles of specialized machinery, and adjusting the technology for feeding, heat processing, and the operational cycle of the pyrolysis furnace to meet the specific requirements of each stage,” shared Associate Professor Dr. Nguyen Minh Ngoc about the calculation process.
Despite the advantages of collaboration and practical research at the factory, solving this problem remains complex. The most challenging aspect lies in operating the rotary pyrolysis reactor at high temperatures in a closed, oxygen-free environment (as the presence of oxygen could cause the gases emitted from the rubber to ignite, leading to dangerous explosions). "Safety must always be our top priority, even above product output and economics," the research team emphasized. As a result, the issue of heat management and synchronized equipment had to be addressed in a unified manner, including investing in the necessary equipment, even expensive imported ones, to meet the required standards.
In addition, the research team also analyzed the technology of cutting tires into small pieces of 2-4 mm (a method used globally, but without specific calculations until now). The results showed that this approach increases the surface area ratio by 97 times, significantly enhancing heat absorption through radiation and conduction, reducing the heat processing cycle by 1-2 hours. Additionally, because the volume of the tire material is reduced when compacted, the capacity for raw materials increases from 12 tons to 15 tons, leading to a higher yield of oil and gas. The feeding technology was also upgraded from manual to automatic, utilizing screw conveyors and extrusion equipment.
The research has demonstrated significant potential to enhance furnace efficiency, reduce fuel costs, and improve the heat exchange and gas collection processes, ultimately increasing oil production. Additionally, the findings underscore the importance of stringent adherence to operational rules when dealing with complex technologies involving pressure, temperature, and safety risks. "Technology operations must be monitored through digital systems on a central control screen, and there must be thorough training for managers, technical staff, and production workers," emphasized Associate Professor Dr. Nguyen Minh Ngoc.
He added, "We have now fully mastered pyrolysis technology, especially in the context of crushed tire pyrolysis, and are prepared to transfer this technology to any units that require it."
Damaged tires are just one type of waste that requires improved treatment efficiency. "There are many types of solid waste with significant environmental impacts, such as plastic waste, garment industry waste, and agricultural by-products like fruit peels, durian shells, coconut shells, pine cones, and rice husks," explained Associate Professor Dr. Nguyen Minh Ngoc. This is the reason why the research team plans to broaden their pyrolysis studies to various solid waste types and investigate the possibility of utilizing carbon black waste from the pyrolysis procedure to develop innovative, eco-friendly materials. Dr. Nguyen Minh Ngoc, for instance, imagines utilizing carbon black waste to manufacture Biochar fertilizer for agricultural purposes.
The research team includes:
Published by Ms. My Hanh from a newspaper published by the Ministry of Science and Technology of Vietnam.
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